This invention relates in general to drive systems for multiple spindle machine tools and in particular to a drive system which employs an independent servo motor which permits matching of spindle speed with tool feed speed.
Multiple spindle machine tools for automatically performing complex machining at high production rates are well known. Typically, these machines have a number of spindles symmetrically arrayed in a spindle carrier which indexes the spindles circularly from one machining station to the next. The workpiece carried in each spindle is subjected to one or more machining operations at each station to produce a finished piece which may be ejected after the machining operations at the final station. The tools for performing the various machining operations are usually carried by movable cross and end slides, the positions and movement of which are controlled by a rotating drum or cam shaft.
Various drive systems for multiple spindle machine tools are employed. Because of the complexity and the automatic nature of the machine operations, some of these drive systems have been developed to a very sophisticated degree. U.S. Pat. No. 3,864,994 entitled "Multiple Spindle Machine With Variable Speed Drive", which is assigned to the assignee of this application, discloses one such sophisticated drive system. The system of the cited patent includes dual sets of change gears to select spindle speed and feed speed for the various machining tools. A high-speed clutch and a feed clutch alternately select either a high speed or a low speed of rotation for a power feed cross shaft which drives the drum shaft. These clutches are controlled by switches actuated by the drum shaft itself, and, typically, the drum shaft rotates about 250 degrees at high speed and about 110 degrees at low speed. To maximize machining time, the high-speed clutch causes traverse of the tool-holding cross and end slides from a fully retracted position to a point adjacent the machining area to occur rapidly. The feed clutch moves the tool at a slower feed rate during the machining operation, the feed rate being related by mechanical interconnection to the spindle rotational speed. The tool continues to move at the feed rate until a limit is reached and it is then returned at a rapid traverse rate to its fully retracted position at which time the spindle carrier indexes.
In addition to the mechanisms and clutches for controlling the high-speed traverse or low-speed feed rate, it is also conventional to provide a reverse clutch to reverse the direction of rotation of the drum shaft if necessary during set-up or in the event of an accident in order that the tools may be withdrawn from the workpieces.
Although the patented drive system and others are adequate and have achieved considerable commercial success, they are rather complex and difficult to build and service. They also involve numerous wearing parts which ultimately require replacement with loss of operating time and increased costs of operations. Moreover, because of the large number of rotating parts, a considerable amount of noise is generated. Attenuation of that noise to meet industry and government requirements can be accomplished only by incorporating suitable guards and sound-absorbing material which adds to the cost of the machine tool.
A principal object of the present invention is to increase the productivity of multiple spindle machine tools by simplifying and increasing the flexibility of their drive systems. Another object of the present invention is to minimize idle time by optimizing the high speed at which tools traverse from a retracted position to a machining position and the speed at which they traverse from the limit of the machining area to the fully retracted position. A further object is to simplify the matching of spindle speeds and tool feed rates during machining operations. A still further object of the present invention is to eliminate complicated gearing and clutches normally utilized for high speed traverse and lower speed feed rates and for reversing operations. Still another object is to avoid the need of noise-attenuating devices and material in machine tools.